When manufacturing a disk drive, concentric servo sectors 60-6N are written to a disk 2 which define a plurality of radially-spaced, concentric servo tracks 6 as shown in the prior art disk format of FIG. 1. A plurality of concentric data tracks are defined relative to the servo tracks 4, wherein the data tracks may have the same or a different radial density (tracks per inch (TPI)) than the servo tracks 4. Each servo sector (e.g., servo sector 64) comprises a preamble 8 for synchronizing gain control and timing recovery, a sync mark 10 for synchronizing to a data field 12 comprising coarse head positioning information such as a track number, and servo bursts 14 which provide fine head positioning information. The coarse head position information is processed to position a head over a target data track during a seek operation, and the servo bursts 14 are processed to maintain the head over a centerline of the target data track while writing or reading data during a tracking operation.
In the past, external servo writers have been used to write the concentric servo sectors 20-2N to the disk surface during manufacturing. External servo writers employ extremely accurate head positioning mechanics, such as a laser interferometer, to ensure the concentric servo sectors 20-2N are written at the proper radial location from the outer diameter of the disk to the inner diameter of the disk. However, external servo writers are expensive and require a clean room environment so that a head positioning pin can be inserted into the head disk assembly (HDA) without contaminating the disk. Thus, external servo writers have become an expensive bottleneck in the disk drive manufacturing process.
The prior art has suggested various “self-servo” writing methods wherein the internal electronics of the disk drive are used to write the concentric servo sectors independent of an external servo writer. For example, a known technique for self-servo writing a disk drive is to first write a plurality of spiral tracks to the disk, and then to servo on the spiral tracks while writing a plurality of servo sectors that define concentric servo tracks such as shown in FIG. 1.